The invention relates to a method and tool for assembling a part to a workpiece with the tool supported on a robot, where a prepared mounting surface of the part is assembled on a prepared target surface of the workpiece, in a thermal plastic welding process, for example.
The invention generally relates to the use of specialized tools or manufacturing processes in the robotic assembly of manufactured components such as automobile parts. In the example used herein, thermal plastic welding of plastic gas tanks for automotive applications is described.
The invention provides an assembly tool that is mounted to a conventional robot and a method of robot assisted assembly as a component of a sequential manufacturing process. The process typically involves a robot that is stationary on a pedestal that selects parts from a tray or other stationary supply and transfers the part to be assembled on a workpiece as the workpiece is conveyed passed the robot, usually in a stepped manner.
A significant advantage of the invention is that cycle time is reduced by simultaneous manufacturing operations carried out by at least two arms on a combination tool resulting in time and cost savings. The combined tool includes means to grip the part, laser scan the workpiece, calculate any offsets required for proper positioning within predetermined tolerances, heating plastic part surfaces and workpiece part surfaces simultaneously, and pressing heated surfaces together to form a thermal plastic weld joint and impervious fluid seal.
It will be understood that plastic welding is used only as an example to describe one application of the invention and that the tool is readily adaptable and equally advantageously used for robot assisted assembly in any number of alternative technologies. For example, the tool can be used for heating plastic surfaces, adhesive application, sealant application, grinding or abrading, or cutting surfaces by replacing the surface preparation modules mounted on the multiple arms of the combination tool. Packaging multiples tools together in a flexible combination tool, that can be easily modified for various applications, provides a much higher degree of flexibility and quick tool change over compared with conventional assembly operations.
In the prior art, welding plastic parts in the automotive industry for example, involves applying heat to the workpiece and/or heat to the part, then exerting sufficient pressure to bond the plastic surfaces together providing a seal and physical joint. Conventional operations utilize two separate tools and two separate robots. One robot with one tool is used for preparation or heating of the workpiece. A second robot and tool is used for preparation or heating of the part, and assembling the part to the workpiece. The capital costs, maintenance and programming involved in operating two separate robots for two separate operations is expensive and undesirable. However manufacturers are under pressure to deliver relatively low volumes of assemblies in decreasing amounts of time due to changes in manufacturing practices, such as xe2x80x9cjust in timexe2x80x9d delivery and extremely low inventory levels. Rapid adaptation and customization of orders is becoming more and more desirable, so the high degree of flexibility obtained through separating robot operations has been considered necessary.
An alternative assembly method is a conventional automated assembly line with separated dedicated fixtures, jigs and tools that prepare the workpiece and part separately and assemble them in a staggered or step wise conveyed fashion. Such dedicated tools are generally less flexible, less expensive and require less technical sophistication than robots. However, these benefits come at the expense of increased cycle time and increased costs in long term operation due to the extensive downtime and cost of changeovers and tool refitting when a new product style is manufactured.
Increasingly, auto parts manufacturers in particular are required to deliver parts to an assembler xe2x80x9cjust in timexe2x80x9d which results in much shorter runs of a particular part design. Rapid tool changeover and rapid adaptation for various styles of assemblies or different assemblies altogether is becoming essential in a highly competitive auto parts manufacturing environment. As a result, the separate dedicated tools that are suitable for long high volume runs at low cost are becoming less and less economically viable whereas processes that provide high degrees and flexibility and rapid changeover for different styles are becoming the norm.
As an example, with separate dedicated tools an automobile part supplier would set up a separate manufacturing line for gas tanks, bumpers, fenders, dashboards and other common components. The economic viability of such specialized lines depends on high volume orders and long production runs, preferably with very little change in the design of individual products or the general layout of the manufacturing facility. Increasingly however manufacturers require delivery of parts from suppliers in smaller volumes and with less lead time than in the past. In addition, pressures to lower costs and speed up tool changeovers are forcing manufacturers to consider much more flexible manufacturing procedures involving robots, component handling and conveyor systems that can be programmed or adapted for multiple functions.
It is an object of the present invention therefore to improve cycle time and process efficiency for manufacturing and assembly operations by utilising combination tools for single robot assisted assembly to replace dedicated one robot/one function tool methods.
It is a further object of the invention to reduce capital expending and improve long term viability of assembly line methods by reducing the number of expensive robots required by utilising tools that have multiple functions and providing simultaneous tool operations thereby reducing cycle time and improving efficiency.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.
The invention provides a method of assembling a part to a workpiece with a combination tool supported on a robot, wherein a mounting surface of the part is assembled on a target surface of the workpiece. The combination tool has a base matching a tool support of the robot that supports a workpiece arm and a part delivery arm. The workpiece arm has a workpiece target surface preparation module and a workpiece target surface scanning module and communicates workpiece target surface position data to the robot. The part delivery arm includes a part gripper capable of releasably holding the part with part mounting surface exposed. A part mounting surface preparation module is supported by the base between: an engaged position in contact with the part mounting surface while the part is held in the part gripper; and a disengaged position retracted from the part mounting surface. An indexing module is supported on the base, and alternates between: a preparation position; and the assembly position, such that: the indexing module in the preparation position supports the workpiece arm aligned on the operating axis while simultaneously supporting the part delivery arm aligned with the part mounting surface preparation module and such that: the indexing module in the assembly position supports the workpiece arm withdrawn from the workpiece while simultaneously supporting the part delivery arm aligned on the operating axis.
The method includes the following steps. (a) Indexing to the assembly position. (b) Picking a part with the part gripper on the part delivery arm from a part supply station. (c) Indexing arms to the preparation position. (d) Operating the workpiece target surface scanning module and communicating workpiece target surface position data to the robot. (e) Moving the robot to set the tool operating axis and calculate tool offsets relative to the position and orientation of the scanned target surface. (f) Simultaneously: engaging the part mounting surface with the part surface preparation module; and engaging the workpiece target surface preparation module with the target surface. (g) Indexing to the assembly position. (h) Using the previously set tool operating axis and calculated tool offsets, engaging the prepared part mounting surface with the prepared workpiece target surface. (i) Releasing the part gripper and withdrawing the tool from the part/workpiece assembly.
By packaging multiple tools in a single combination tool, and enabling simultaneous operation, the cycle time of the assembly process is reduced. Conventional robot assembly systems often use separate tools on separate robots for each function. Using combination tools not only permits reduction in capital costs associated with each robot, but also reduces cycle time by using the same positioning offset data to be used by the robot to position each tool of the combination array. Conventional redundancies are eliminated, in the physical need for multiple robots, redundant robot motions are avoided and scanned position data redundancy is avoided by using the same positioning data for operating each tool.
Further advantages of the invention include reduction in assembly area size through use of compact combination tools and single robots, reduced tool changeover time, and increased accuracy and reliability through elimination of robot movements and multiple positioning operations.